Antenna



June 20, 1950 J. H. GARDNER ANTENNA Filed Mar 'ch 22, 1945 PIC-5.2

FIG.5

' INVENTOR. JOHN H. GARDNER ATTORNEY Patented June 20, 1950 UNITED STATES PATENT OFFICE John H. Gardner, Cambridge, Mass, assignor, by

mesne assignments, to the United States of I America. as represented by the Secretary of War Application March 22, 1945,' Serial No. 584,228

1 This invention relates object-locating systems and particularly to means for'obtain-ing a radiationpattern closely approximating the relationship csc din one plane, where is the angle measured from'the axis of the radiati-ng means.

In certain radio object-locating systems, for example, ground search apparatus or low-altitude airborne sets, it is desirable thatthe distribution of energy in a vertical plane throughout a relatively wide angle be such that the variation of energy density versus the radiation angle is a cosecant-squared function. This provides relatively constant echo strength for targets located on the earth or other surface or at equal altitudes in space regardless of whether the target is distant or close in, and it eliminates the need of tiltingthe antenna to obtain adequate coverage of the area under observation.

The present invention contemplates an economical and quick method of altering a usual type of parabolic reflector such as a paraboloidal dish to obtain a different type of energy distribution patternsuch as a pattern of csc 0 configuration, preferably having a-relatively elongated base line, and with a relatively high gain compensating for less angular coverage.

Accordingly, one of the objects of the present invention is to afford a cosecant-squared radiation pattern by modification of the usual type of I paraboloidal reflector. Another object of the invention is to provide a quick and convenient means of altering a usual paraboloidal reflector without disturbing the original reflecting surface.

Still another object of this invention is to provide amember which is adapted to be attached to at least one portion of a usual type of paraboloidal reflector for presenting a reflecting surface angularly related to that of the paraboloidal surface whereby a beam of energy is adapted to be reflected in a pattern having a modified cosecantsquared configuration.

Other objects and advantages of the invention will become apparent as the description proceeds.

In the drawing:

Fig. 1 is a partially diagrammatic side view of an antenna embodying the reflector according to the invention;

Fig. 2 is a front elevation of the same;

Fig. 3 is an enlarged perspective side view of the upper half of the reflector showing structural features thereof according to one embodiment of the invention;

Fig, 4 is a diagrammatic side view showing the 6 Claims. (01. 250-3355) to antennas for radio radiation patterns produced respectively by' the parabolic reflector of Figs. 1 and 2=When used 'in the conventional manner and in the modified form according to the present invention; and if Fig. 5-i's-a front elevation view' showing another modificationof my invention wherein the sheet member is mounted in the lower half of the refle'cting surface. I Referring to Figs, 1 and 2 of the drawing, a radiating -'element or source. I l) such as 'a dipole and parasitic element, fed by a wave guide or coaxial'line' H, is constructed and located in a conventional manner for illuminatinga reflector I2. Reflector I 2 isformed preferably as aparabolo'idal surface having its focal point at the apparent center of radiation of the radiation source or element IE3. As is well known the reflector -I2, as thusfar described, is adapted to reflect radiant energy in a-penciltype beam characteristically having a distribution pattern relativel narrow both'in elevation and azimuth,'as indicated by the solid line configuration in Fig. 4. w l A- member I3; comprising a curvedstrip or shee of metal, is adapted to be mountedin front of and to extend substantially horizontally across at least a portion of the upper half of reflector I2. Sheet member [3- has: relatively long parallel upperand 'loweredges l4 and I5 respectively and relatively short side edges I6 which may be sloped or shaped to conformgenerallylwith the adjacent edges of reflector I2. 'The width of'strip member 1.3:,1311217 is .the distance between edges I4 and I5, is preferably more than awavelength of the radiant energy. a v

Whenitis desired that reflector I2 be modified to obtain "a'beam of csc *0 configuration, member I:3.- is :placed inelfective position in front of reflector I2. The lower edge I5 of the r-nember-is attached to reflector I2 in abutting relation along the surface for substantially the full width thereof and preferably slightly above the vertex or focal line F so that lower edge I5 isin a plane substantially parallel with a horizontal plane through the focal line F. The surface of member I3 is arranged or disposed at an angle a (Fig. 1) to the surface of reflector I2 such that the average spacing between member I3 and reflector I2 is preferably about one-eighth of the wavelength of the radiant energy to obtain the optimum phase relationship between member I3 and reflector I2. Accordingly, the distance between reflector I2 and the upper edge I4 is approximately a quarter of the wavelength of the radiant energy.

Member I3 may be secured in the effective posi or slots I9 in the adjacent edge portions of re-,

effective shape of reflector I2 asdesired.

It will be seen that when member I3 is placed in the aforesaid position, it serves to modify the reflecting surface of the upper half of reflector l2 while the lower half of reflector I2 remains a parabolic surface. Thus, member I3 effectively forms the upper portion of modified reflector I2 and tends to concentrate the radiation downwardly while the lower half of reflector I2 tends to concentrate the radiation ahead of reflector I2. The combination of these effects is such as to produce the type of radiation pattern indicated in broken lines in Fig. 3 which closely approximates the relation csc 0, where 6 is the radiation angle measured from the radiation axis 0=0. It will be appreciated that a circular or PPI type scan to which the present invention may be applied, may be accomplished by rotation of the antenna about a vertical axis in a well known manner. Distant objects located in the area which is being scanned are subjected to radiant energy by a portionof the radiation field having relatively greater intensity than that portion of the radiation field which impinges upon objects closer in, whereby substantial uniformity in the strength of received signals is achieved. It will be appreciated that modifications in the shape and angular relation of sheet member I3 can be made, if desired, to alter the cosecantsquared pattern.

While the above description has disclosed that the sheet member I3 is placed above the vertex or focal line of the reflector, it will be understood that the sheet member I3 may also be located below the vertex as shown in Fig. 5. In this latter position member I3 tends to concentrate the radiation in an upward direction and thus the. reflector may produce an upwardly directed beam of csc? 0 configuration.

Various other modifications and improvements may be made within the scope of the present invention and therefore it is not desired that the invention be limited to the precise details set forth herein.

What is claimed is:

1. An antenna comprising a paraboloidal reflector, a, radiating means disposed at the focal point thereof, and a sheet-like arcuate member mounted in front of the reflecting surface, said sheet-like member having relatively long parallel upper and lower edges and relatively short side edges, said member having its lower edge attached along the full width of said reflector in a line slightly above and substantially parallel to a horizontal plane through the axis of said reflector and said upper edge being spaced from said reflector one-quarter of the wavelength of i the radiant energy, whereby said sheet-like memher is angularly related to the adjacent portion of said reflector and affords a modified reflecting surface in conjunction with the lower half of said reflector for producing a radiation pattern which varies as the square of the cosecant of the angle measured from the radiation axis of the antenna.

2. An antenna comprising a paraboloidal reflector, a radiant energy transducer disposed at the focal point thereof, and a sheet-like arcuate member mounted in front of the reflecting surface for modifying the radiation pattern emanating therefrom to produce a cosecant squared beam, said member having relatively long parallel upper and lower edges and relatively short side edges, one of said parallel edges abutting said reflecting surface for substantially the full width thereof, and the other of said parallel edges being spaced a predetermined distance from said reflecting surface.

3. An antenna as claimed in claim 2, wherein the abutting edge of said sheet-like member is the lower parallel edge.

4. An antenna as claimed in claim 2, wherein the average spacing between said member and said reflecting surface is one-eighth of the wave length of the radiant energy.

5. An antenna, as claimed in claim 2, wherein the spacing between the upper and lower parallel edges of said sheet-like member is at least a wave length of the radiant energy.

6. An antenna as claimed in claim 2, wherein said member is mounted in front of a portion of the lower half of said reflecting surface.

JOHN H. GARDNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Peterson June 23, 1942 

